HR: 0800h
AN: B21A-1018    [Abstracts]
TI: Evidence for Bacterial Sulfate Reduction in a Fissured-porous Karst System in Southern Germany
AU: * Einsiedl, F
EM: einsiedl@gsf.de
AF: GSF-National Research Center for Environment and Health, Institute of Groundwater Ecology, Ingolstaedter Landstrasse 1, Neuherberg, 85764 Germany
AU: Mayer, B
EM: bernhard@earth.geo.ucalgary.ca
AF: University of Calgary, Department of Geology and Geophysics, 2500 University Drive NW, Calgary, Alb T2N 1N4 Canada
AB: Twenty five percent of the world's population uses karst water as drinking water resources. Since karst groundwater systems are highly vulnerable to contamination, groundwater protection and self purification is a major challenge. Up to now research in karst groundwater systems has predominantly concentrated on hydrodynamic processes. Little is known about anoxic processes in oxygen dominated, fracture-matrix diffusion controlled karst aquifers. Isotope measurements comprise a promising tool to identify biogeochemical processes such as bacterial (dissimilatory) sulfate reduction in karstic aquifers. The goal of this study was to determine the sources and the processes affecting sulfate in an oxygen-rich karst aquifer in southern Germany and their dependence on hydrogeological parameters. This was achieved by interpreting tritium data with a simple lumped parameter approach and assessing variations in concentrations and isotopic compositions of sulfate and dissolved inorganic carbon (DIC) with respect to groundwater age. Young groundwater (<30 years) was characterized by comparatively high sulfate concentrations (0.36 mM) and δ³⁴S values similar to those of recent atmospheric deposition (1.5‰). In contrast groundwater with mean residence times >60 years had significantly lower sulfate concentrations (0.08 mM) and markedly higher δ³⁴S values (7.5‰). These results indicate that in karst systems with matrix porosity, bacterial (dissimilatory) sulfate reduction may occur. This process has the potential to contribute to long-term biodegradation of contaminants in the porous rock matrix representing the dominant water reservoir in fissured-porous karst aquifers.
DE: 1030 Geochemical cycles (0330)
DE: 1041 Stable isotope geochemistry (0454, 4870)
SC: Biogeosciences [B]
MN: Fall Meeting 2005